The production of shaped articles from foamed olefin polymers involves a process which includes admixing an olefin polymer, an organic peroxide and a gas generating compound, extruding the resultant composition into a flat sheet and feeding the flat sheet through an oven which is at a temperature sufficiently high to activate the organic peroxide and gas generating compound. Activation of these materials, serves to foam and thermoset or cure the sheeted composition to a crosslinked density which allows the foamed sheet to be subsequently thermoformed into a shaped article of desired configuration. The density of the foamed sheet is controlled, by adjustment of process parameters, including amount of organic peroxide and gas generating compound, to a level such that the blowing agent gases generated are retained in the composition and are able to expand the composition to the maximum extent.
It has been found, however, that due to a relatively low crosslinked density, foamed articles produced by the process described, lack the dimensional stability required to be successfully used, for example, as liners for automobile trunks and the like wherein relatively high temperatures are encountered. In an attempt to improve the dimensional stability of foamed articles, it has been suggested to increase their crosslinked density by increasing the level of organic peroxide in the basic compositions. This expedient has not proved to be particularly effective as a higher level of organic peroxide tends to restrict the level of expansion of the compositions involved and renders the resultant foamed sheets more difficult to thermoform. Attempts to alleviate problems, caused by a higher level of organic peroxide, by adding more gas generating compound has only increased the cost of the overall process and final product.